/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.view.tiles3;

import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.tiles.TilesException;
import org.apache.tiles.preparer.PreparerException;
import org.apache.tiles.preparer.ViewPreparer;
import org.apache.tiles.preparer.factory.NoSuchPreparerException;

import org.springframework.util.ClassUtils;
import org.springframework.web.context.WebApplicationContext;

/**
 * Tiles {@link org.apache.tiles.preparer.PreparerFactory} implementation
 * that expects preparer class names and builds preparer instances for those,
 * creating them through the Spring ApplicationContext in order to apply
 * Spring container callbacks and configured Spring BeanPostProcessors.
 *
 * @author Juergen Hoeller
 * @see SpringBeanPreparerFactory
 * @since 3.2
 */
public class SimpleSpringPreparerFactory extends AbstractSpringPreparerFactory {

    /**
     * Cache of shared ViewPreparer instances: bean name -> bean instance
     */
    private final Map<String, ViewPreparer> sharedPreparers = new ConcurrentHashMap<>(16);


    @Override
    protected ViewPreparer getPreparer(String name, WebApplicationContext context) throws TilesException {
        // Quick check on the concurrent map first, with minimal locking.
        ViewPreparer preparer = this.sharedPreparers.get(name);
        if (preparer == null) {
            synchronized (this.sharedPreparers) {
                preparer = this.sharedPreparers.get(name);
                if (preparer == null) {
                    try {
                        Class<?> beanClass = ClassUtils.forName(name, context.getClassLoader());
                        if (!ViewPreparer.class.isAssignableFrom(beanClass)) {
                            throw new PreparerException(
                                    "Invalid preparer class [" + name + "]: does not implement ViewPreparer interface");
                        }
                        preparer = (ViewPreparer) context.getAutowireCapableBeanFactory().createBean(beanClass);
                        this.sharedPreparers.put(name, preparer);
                    } catch (ClassNotFoundException ex) {
                        throw new NoSuchPreparerException("Preparer class [" + name + "] not found", ex);
                    }
                }
            }
        }
        return preparer;
    }

}
